Pleasure craft

ABSTRACT

The present invention relates to a craft comprising a surface module, a single submerged body and a one strut for connecting the body to the module, wherein said strut is operative for moving the submerged body relative to the surface module from a extended position of the body in which the surface module is arranged in vertically spaced relation thereabove to a retracted position in which the submerged body and the surface module together form a displacement hull, wherein the hull of the surface module comprises a hollow recess for receiving the submerged body in the retracted position, wherein the recess and the upper part of the submerged body have a mating form such that the hull of the craft in the retracted position of the submerged body has a drag reducing form.

[0001] The present invention relates to craft comprising a surfacemodule, a single submerged body and a strut for connecting the body tothe module, wherein said strut is operative for moving the submergedbody relative to the surface module from a extended position of the bodyin which the surface module is arranged in vertically spaced relationthereabove to a retracted position in which the submerged body and thesurface module together form a displacement hull.

[0002] Traditionally, ship hull shapes can be classified in threecategories: displacement designs, semi-displacement designs and planinghigh speed designs. The maximum speed for displacement designs islimited by the wave system generated, whereas semi-displacement designscan enter the planing state using much power and generating excessivewaves. In the planing state, the crests of surface waves will result invertical acceleration of the hull, which has a direct influence onpassenger comfort. High speed hull shapes have poor low speed efficiencyin terms of kg fuel/m and the efficiency at cruising speed is at bestsimilar to the efficiency at top speed. Innovative designs likehydrofoils or small water area twin hull crafts enable high speedswithout compromising passenger comfort in a sea state but have importantdisadvantages. The disadvantages are among others a notably complicatedpropulsion, big exposed hydrofoils in case of the hydrofoil designs and,in case of a twin hull craft, habitable volume lost between the hullsand a beam that is less suited for harbors with a traditional layout.

[0003] A combination of hydrofoils and a central submerged body, i.e. ahydrofoil small water area ship, can result in a craft with a propulsionof high efficiency because of the possibility to place a propeller in aapproximately uniform flow field of water accelerated by surface drag.In such a craft the hydrofoils can be designed not to extend beyond thebeam of the hull, whereas no habitable volume is lost. Such a design isknown from U.S. Pat. No. 3,730,123. However an optimization of habitablevolume and draught as well as energy efficiency for the different speedranges is not achieved.

[0004] For ship carrying passengers, the required habitable volume isdirectly related to the purpose of the ship (how many passengers andcrew, what kind of voyage at which comfort level) and in the conceptphase maximized within practical and aesthetic limits. A shallow draughtcan dramatically increase the area of inland waterways which can benavigated. Inland waterways are, for the average passenger, much moreattractive than the open sea. A comparatively high cruise speed with ahigh comfort level in an average sea state can increase the area of theglobe that can be reached within a constrained period (e.g. a holidayperiod). Thus, the craft should ensure safety, passenger comfort orminimization of wave generation for all speed ranges, energy efficiencyand exciting maneuverability.

[0005] According to the invention these objectives are met with a craftcharacterized in that the hull of the surface module comprises a hollowrecess for receiving the submerged body in the retracted position,wherein the recess and the upper part of the submerged body have amating form such that the hull of the craft in the retracted position ofthe submerged body has a drag reducing form.

[0006] In retracted position the surface area of the recess of thesurface module and the surface area of the upper part of the submergedbody and the surface area of the struts have no contact with a boundarylayer of water. As a consequence these area's have no relevantcontribution to surface drag and overall surface drag is relatively low.Furthermore minimal draught is obtained with a predetermined minimumstanding height.

[0007] It is noticed that U.S. Pat. No. 3,590,765 discloses areconfigurable vessel comprising a surface hull module and a submergedbody connected thereto by means of two struts which can be actuated tolower the surface hull module to seat on the water surface in order toreduce draft of the vessel for navigating in shoal water or for docking.This vessel however does not have a conformal recess for receiving (partof) the submerged body.

[0008] Preferably the recess is further recessed at the aft section ofthe surface module for receiving a propeller mounted to the submergedbody in the retracted position thereof. When the submerged body isretracted, the massive flow disturbance for the propeller caused by thehull can be prevented by incorporating a streamlined further recessedpart in the conformal recess enabling an additional flow around thesubmerged body with the result of an even flow-field for the propeller.The aft recess has a narrowing part downstream of the propeller toensure a positive pressure at the top and to prevent ventilation of thepropeller resulting in a loss of thrust. Strakes arranged along theedges of the aft recess in the hull prevent parasitic resistance due towater flowing into the aft recess. For steering the craft in a slowspeed mode a rudder is attached to the surface module. The rudder islocated in the wake of the propeller in the retracted position of thesubmerged body.

[0009] The submerged body has preferably a raised bow to improvepressure distribution with a positive effect in the near surface flow.Furthermore the body has a streamlined shape with a flattened circularcross-section being axi-symmetrical at the stern. The cross-section isflattened to ensure that the standing height and draught constraints arenot exceeded.

[0010] To enable different modes during navigation, the submerged bodycomprises at least two pairs of hydrofoils, said pairs being mounted tothe submerged body along the length thereof, whereas the hydrofoils ofeach pair are attached on both sides of the submerged body. Next to aslow speed mode (or full displacement mode), a planing mode and a foilborn mode can be obtained. When changing from slow speed mode to foilborn mode, the submerged body is extended by operation of the struts.The place of attachment of each hydrofoil on the submerged body isdetermined dependent on the pressure build-up generated by water flowalong the submerged body in extended position. The placement of thehydrofoils should be such that they positively influence the wavepattern generated.

[0011] In a preferred embodiment a winglet is fitted to the tip of atleast the aft pair of hydrofoils to reinforce them. When the hydrofoilsof each pair are arranged in a negative dihedral, the tips can be placedon the ground to support the craft on the ground in a leveled dried upposition or in shallow water harbors, e.g. to raise the hull of thesurface module above water level to prevent bio-fouling.

[0012] In a further preferred embodiment each hydrofoil is rotatablearound its longitudinal axis. The rotatable hydrofoils are set tooptimum angles to minimize overall drag and reducing the waves generatedwhen the craft is not in a foil born mode.

[0013] Directional control for low speed conditions is ensured by alow-speed rudder attached to the surface module in the wake of thepropeller when the submerged body is retracted. The helmsman can selecta switch so that at or above a predetermined transition speed thecontrol system can quickly select an angle of attack setting for foilborn mode. A fast selection limits the energy lost in the transitionwhere the hydrofoils have considerable profile drag and induced drag andwhere the surface and pressure drag of the surface module is still high.In foil born mode the hydrofoils are controlled to retain straight andlevel “flight” or to (partially) follow the contour of long (ocean)waves or to make turns according to inputs from the helmsman ornavigation system. As a method to maximize the excitement of the ride,the control system determines safety constraints of immersion and(aggressive) bank following from joystick inputs. This system can evenallow the craft to jump. In the system, foil surface breaking withresulting ventilation and loss of lift is monitored and predicted tosafeguard spin out situations.

[0014] The center of gravity and the floatation center for the craftwith an extended submerged body ensure a positive righting arm for allpositions. When a negative righting arm for a craft with a retractedbody is considered a problem, the craft can be fitted with an emergency“extend” function. The control systems furthermore monitors and predictsthe breaking of the surface by the propeller and regulates the powergenerated by the generators and the excitation of the electric motor toprevent overspeed conditions. Apart from that, the control system canselect an angle of attack for each hydrofoil pair that results in anemergency stop. In such a situation the hull takes a nose up position sothat deceleration and gravity combine to an acceleration vector normalto the deck which prevents passengers from falling or being launchedfrom their seats.

[0015] The nose of the submerged body is provided with an integratedwater tank having a closure shaped as a nozzle and provided with a capwhich breaks at a predetermined pressure. When the submerged body of thecraft hits an object the nose will compress and the pressurized waterpasses through the nozzle shaped closure to the surrounding. The outflowof high pressure water will absorb the impact energy and prevent seriousdamage to the craft. Also the attachment of the struts to submerged bodyis calculated to break off at a predetermined strain level which can beabsorbed by the hull construction. This will further reduce the riskthat impacts at high speeds result in a loss of the craft.

[0016] To summarize, the invention can result in embodiments that bettermeet the objectives than all previous hull shapes and hydrofoilarrangements.

[0017] The present invention will be further elucidated with referenceto the accompanying drawings. In the drawings shows:

[0018]FIG. 1 a preferred embodiment of a craft comprising a surfacemodule and a retracted submerged body;

[0019]FIG. 2 the surface module of FIG. 1 with an extended submergedbody;

[0020]FIG. 3 a side view of the craft with the retracted submerged body;

[0021]FIG. 4 a side view of the craft with the extended submerged body;

[0022]FIG. 5A a front view, FIG. 5B a back view and FIG. 5C a partiallyside view of the submerged body;

[0023]FIG. 6 a cross-section of the craft near the recessed aft section;

[0024]FIG. 7 a longitudinal section of the recessed aft section;

[0025]FIG. 8 wave patterns generated by the submerged body and thehydrofoils in foil born mode;

[0026]FIG. 9 the hydrofoil dihedral in a banked turn;

[0027]FIG. 10 the craft in a dried up position;

[0028]FIG. 11 the craft with extended submerged body in a harbor;

[0029]FIG. 12 wave patterns generated by the submerged body and thehydrofoils in a low speed mode;

[0030] FIGS. 13A-D different angle settings of the hydrofoils;

[0031]FIGS. 14A en 14B side views of the submerged body with crushablenose;

[0032]FIG. 15 a breakage of the connection between the struts and thesubmerged body;

[0033]FIG. 16 an emergency stop maneuver;

[0034]FIG. 17 a jump maneuver;

[0035]FIG. 18 placement of sensors and input devices;

[0036]FIG. 19 a schematic overview of a navigation and control system;

[0037] The shape of the craft according to the invention is generallyshown in FIGS. 1-4. The craft comprises a surface module 1, a singlesubmerged body 2 and two struts 5 for connecting the body 2 to themodule 1. The struts 5 are operative for moving the submerged body 2relative to the surface module 1 from a retracted position (FIGS. 1 and3) to a extended position (FIGS. 2 and 4) of the body 2.

[0038] The surface module 1 has a recess 6 conformal to the uppersection 3 of the submerged body 2. In the extended position of thesubmerged body 2, the recess 6 is exposed to waves but will not impairdirectional stability nor induce vertical loads (wave slam) because ofthe linear edge and smooth curved shape. Two pairs of hydrofoils 4, 12are attached to the submerged body 2. One pair 12 at the front part andone pair 4 at the aft part of the submerged body 2. The hydrofoils 4, 12of each pair are located on both sides of the submerged body 2.

[0039] The submerged body 2 has a central high-skew propeller 8 drivenby an electrical motor which is powered by generators in the surfacemodule 1. The length of the submerged body 2 should be such that theposition of the two pairs of hydrofoils 4, 12 can have the desiredinfluence on the wave pattern induced by the submerged body and that theinfluence on the flow field in front of the propeller 8 is not to muchdisturbed. Also the front of the submerged body should be somewhat cutback from the bow of the surface module to prevent damage when mooring.This will result in a submerged body 2 which is somewhat shorter thanthe surface module 1. The optimum diameter/length ratio for a submergedbody 2 with a given displacement resulting in a minimum surface drag andpressure drag will result in an unpractical large diameter. The diameteris constrained by the requirement of a flat passenger's floor 9 being aslow as practical to ensure adequate vertical space without gainingundesirable high deckhouses, and the requirement of a shallow draught asdetermined by the water line 10 and the keel line 11 of the craft (seeFIG. 3). The submerged body 2 has a bow and stern part connected by along part with a parallel top line 13 and keel line 11.

[0040] When in foil born mode the control system will steer thehydrofoils 4, 12 (FIG. 4). The level of the surface module 1 in relationto the water surface (with an average water line 10 as indicated in FIG.4) is maintained in such a way that instances of waves touching the hullof the surface module and ventilation of hydrofoils 4, 12 or propellerin troughs between wave crests are minimized. When the length andfrequency of the waves, as sensed by the control system, are suitable awave contour “flight” path can be followed.

[0041] An axi-symmetrical streamlined submerged body 2 can be an optimalchoice when optimizing for performance and endurance. A streamlinedsubmerged body with a bigger volume and better (near-surface) pressuredrag performance is shown in FIG. 5. The submerged body retains theaxi-symmetrical stern 19 (FIG. 5A) with the integrated propeller and thebow 20 is raised (FIG. 5B and C) to improve pressure distribution with apositive effect in near surface flow. The submerged body 2 has aflattened circular cross-section. Finally, placement of the fronthydrofoils 12 can be optimized for cruise speed so that the low draglaminar flow conditions can extend for a significant part of thesubmerged body.

[0042] The boundary of the recess 6 in the hull of the surface module isindicated with reference number 24 in FIG. 6. The recess 8 is furtherrecessed at the aft section of the craft (see upper drawing in FIG. 6)such that a streamlined aft recess 23 is obtained. This aft recess 23enables an additional flow around the streamlined body resulting in aneven flow-field for the propeller 8. FIG. 6 shows a cross-section justin front of the propeller hub, whereas FIG. 7 shows a longitudinalsection just above the centerline of the submerged body. The aft recess23 has a narrowing part 26 downstream of the propeller 8 to ensure apositive pressure at the top of the aft recess 23 (which is at waterlinelevel) and prevent ventilation of the propeller. The hull is fitted withtwo strakes 27 which prevent loss of dynamic pressure for the downstreamflat surfaces of the hull when the craft is in a (non foil born) planingmode.

[0043] In foil born mode the flows around the submerged body and theflows as influenced by the hydrofoils 4, 12 generating lift can beinfluenced by the shapes and angle setting of these parts such thattheir interaction has a positive result on the overall wave drag (andwave energy causing damage and nuisance). This is depicted in FIG. 8.Line 29 is a section through the wave pattern as generated by thesubmerged body. Line 31 is a section through the wave pattern asgenerated by the pairs of hydrofoils 4, 12 and line 30 is a sectionthrough the wave pattern for the combination of the submerged body 2 andthe hydrofoils 4, 12.

[0044] To meet the objective for an exiting high-speed maneuverabilitythe hydrofoils 4, 12 are placed in a negative dihedral to preventventilation when making steep turns. To make the turn as steep aspossible an edge 32 of the hull can touch the water (see FIG. 9). Theangles for the aft 4 and the front 12 hydrofoils are indicated withreference numbers 34 and 33 respectively. Furthermore the dihedral isused for small yaw corrections.

[0045] The negative dihedral helps in providing support in drying upconditions (see FIG. 10). The control system has an algorithm to adjusthydrofoil angles and to move the submerged body relative to the surfacemodule when preparing for a dried up position. A similar algorithm canbe used in the harbor (see FIG. 11) to raise the surface module abovethe water level. To increase the strength of the hydrofoil tips awinglet shaped element 35 is fitted to each aft hydrofoil 4. Whenproperly shaped this winglet 35 has some positive effect on hydrodynamicperformance.

[0046] To minimize drag in the low-speed mode (see FIG. 11) the anglesof the hydrofoils 4, 12 are being set in such a way that the interactionof the pressures generated by the hull of the surface module incombination with the retracted submerged body and the pressuresgenerated by the hydrofoils at this determined setting is optimized.These pressures result in waves. In FIG. 12 these waves are indicated bysection line 38 for the surface module with submerged body, section line40 for the hydrofoils at angles 41, 42 and the resulting section line39. In this mode the control system can give inputs to the hydrofoils toincrease roll stability The hydrofoils are movable around theirlongitudinal axes standing at right angels to the submerged body. Thefront hydrofoils 12 and the aft hydrofoils 4 are shown in FIG. 12.

[0047] The collapsible forward section of the submerged body is shown inFIG. 13. When a hard object 51 hits the submerged body, the frontsection 50 compresses and water 49 is forced through the nozzle shapedclosure 48. The forward bulkhead 47 is strong enough to retain itsintegrity even when hitting objects at top speed. However at top speedthe loads on the structure will be such that structural damage isinevitable. To prevent the connection between the struts 5 and thesurface module 1, which contains moving elements, from failing and theunderside of the hull potentially tearing with a high risk of losing thecraft, the connection between the struts 5 and the submerged body 2 isdesigned such that in case of high deceleration forces being transmittedto the surface module 1 the struts 5 can rotate (see FIG. 15). Thisrotation induces uneven shear forces to the shear-pins 52, 53 thatconnect the struts 5 to the submerged body 54. As a result theconnection fails leading to a separation of the submerged body 2 and thesurface module 1.

[0048] The control system enters an emergency stop sequence when thethrottles are slammed back in foil born mode (see FIG. 16). Thegenerators are throttled and the electric motor is slowed down withinlimits to prevent damage to the motor or propeller. The aft hydrofoils 4are set to induce a pitched angle of the craft so that the resultingvector 56 from the dynamic and static forces of the water on the craftresult in a force acting on the passengers not deviating from normalgravity. The front hydrofoils 12 are set to maintain a certain depth inthe water to prevent ventilation. The craft makes a planing “landing” onthe rear end of the hull.

[0049] The control system sets limits to an envelope for radicalmaneuvers under helmsman control. FIG. 17 shows a jump maneuver. Comingfrom the normal “flight” depth 57, the helmsman lowers the craft 58,makes an aggressive pull up 59 when there is enough vertical speed toclear the water surface 60 and than make a splash landing 61.

[0050]FIG. 18 indicates the location of the non-standard sensors and theinput devices. The four antennae 62, 63, 64, 65 of the GlobalPositioning System (GPS) are placed on the roof of the pilothouse inoptimal view of overhead GPS satellites. The combined three-axis angularrate sensor 66 is located near the center of gravity at the level ofpassengers sitting in the craft. The submerged body immersion (watersurface distance) sensors 69, 81 are located near the tip of thesubmerged body facing towards the surface. The input devices are ajoystick 67 for bank (and consequent turn) and depth input and athrottle 68 for revolutions of the propeller and emergency stop input.The joystick 67 has a trim button for trimming the craft in case of anunavailability of the GPS attitude. Switches and buttons are not show.

[0051]FIG. 19 indicates the navigation and control system. Extended orretracted mode is selectable in the control panel 89. Using this controlpanel 89 also autopilot having different options and the controlparameters which determine comfort level and energy use can be selected.The control parameters are for example “comfort” meaning minimizedaccelerations, “economy” meaning minimized hydrofoil angle changes, and“performance” meaning maximised safe turn rate and jump capability. Alsospecial functions, such as levelling when drying up, can be selected andsystem condition and maintenance information are presented in thecontrol panel. The control systems has a dual redundant architecturewith two controllers 87 and 88, each using different input signals.Controller 87 obtains input signals from the xyz-roll rate sensor 66,immersion sensor 69, speed sensor 86 and joystick 67, whereas controller87 obtains the input signals GPS-attitude and speed from GPS antennae62-65 and further input signals from immersion sensor 81 and joystick67. Both controllers 87, 88 are connected to the control unit focontrolling the four hydrofoils 90-93. The control unit comprises fourduplex integrated servo actuator 94-97 which control the angularposition of hydrofoil 90-93 respectively. A processor 83 is used for theman-machine interface, interfacing to other systems and systemmonitoring. This processor 83 connects to the different system elementsthrough a network, schematically depicted as 98 and has a standardised(NEMA) network interface 99. Both sides of each duplex integrated servoactuator 94-97 have a separate power supply. The control system is setup in such a way that failure of a single controller 87, 88, the network98, the processor 83 or one side of a duplex integrated servo actuator94-97 will not preclude foil born navigation (with certainrestrictions). For an extended non-foil born mode, an extended foil bornmode and retracted slow speed mode different settings and limits areused. The joystick 67 has a “foil born” switch so that, when selected,the controllers 87, 88 switch the hydrofoils 90-93 settings when thespeed through the water reaches the predetermined transition speed. Thecontroller 88 monitors wave-height and wavelength measured by thesubmerged body immersion sensor 81 in combination with GPS. Whenwavelength, wave-height and periodicity are suitable, a “Soll” flightpath following a wave contour is established. The information on thewave situation is monitored by the processor 83 and control limits areapplied to the selection (or automatic de-selection) of the performancesettings.

[0052] The invention relates to a ship configuration which is variable.There is provided a craft with a retractable submerged body fitted withmovable hydrofoils controlled by a full authority control system tooptimize three speed ranges, namely a low speed displacement mode (withthe submerged body retracted), a cruise mode where the main hull islifted above water surface and lift is generated partly by flotationforces and partly by the hydrofoils, and a high speed mode where thehydrofoils enable tight control on safety margins and passenger comfortand high maneuverability.

[0053] While the foregoing description and accompanying drawingsrepresent preferred embodiments of the present invention, it will beobvious to those skilled in the art that various changes andmodifications may be made therein without departing from the spirit andscope of the present invention.

1. Craft comprising a surface module, a single submerged body and a onestrut for connecting the body to the module, wherein said strut isoperative for moving the submerged body relative to the surface modulefrom a extended position of the body in which the surface module isarranged in vertically spaced relation thereabove to a retractedposition in which the submerged body and the surface module togetherform a displacement hull, characterized in that the hull of the surfacemodule comprises a hollow recess for receiving the submerged body in theretracted position, wherein the recess and the upper part of thesubmerged body have a mating form such that the hull of the craft in theretracted position of the submerged body has a drag reducing form. 2.Craft according to claim 1, wherein a propeller is mounted to thesubmerged body and wherein the recess in the surface module is furtherrecessed at the aft section thereof for receiving the propeller in theretracted position of the submerged body.
 3. Craft according to claim 2,wherein strakes are arranged along the edges of the further recess inthe hull.
 4. Craft according to one of the preceding claims, wherein arudder is attached to the surface module, said rudder being located inthe wake of the propeller in the retracted position of the submergedbody.
 5. Craft according to one of the preceding claims, wherein thesubmerged body has a raised bow and a streamlined shape with a flattenedcircular cross-section being axi-symmetrical at the stern.
 6. Craftaccording to one of the preceding claims, wherein the submerged bodycomprises at least two pairs of hydrofoils being mounted to thesubmerged body along the length thereof, the hydrofoils of each pairlying on both sides of the submerged body.
 7. Craft according to claim6, wherein the place of attachment of each hydrofoil on the submergedbody is determined dependent on the pressure distribution generated bywater flow along the submerged body in extended position and/or vortexgeneration around the hydrofoils.
 8. Craft according to claim 6 or 7,wherein a winglet is fitted to the tip of at least the aft pair ofhydrofoils.
 9. Craft according to one of the claims 6-9, wherein thehydrofoils of each pair are placed in a negative dihedral.
 10. Craftaccording to one of the claims 6-9, wherein each hydrofoil is rotatablearound its longitudinal axis.
 11. Craft according to one of thepreceding claims, wherein the bow section of the submerged bodyplastically deforms when hitting a obstacle.
 12. Craft according toclaim 11, wherein the bow section is provided with a tank filled withwater and bounded with a nozzle shaped closure which opens at apredetermined pressure in the tank.
 13. Craft according to one of theclaims, wherein the connection between the strut on the one side and thesubmerged body and/or the surface module on the other side fails at apredetermined impact level upon hitting an obstacle.
 14. Craft accordingto one of the claims 6-13, further comprising a control unit forcontrolling the rotation of each hydrofoil.
 15. Craft according to claim14, further comprising xyz roll rate sensors for providing xyz roll rateinformation of the craft.
 16. Craft according to claim 15, furthercomprising a GPS for providing Lat/Long, attitude and directionalinformation of the craft.
 17. Craft according to claim 16, wherein thexyz roll rate information is used as input signal and the GPSinformation is used as reference signal of the control unit.
 18. Craftaccording to claim 16, wherein the xyz roll rate information is used asinput signal of a rate input controller and wherein the GPS informationis used as input signal of an attitude input controller, saidcontrollers providing dual redundant input signals for the control unit.19. Craft according to claim 18, wherein the control unit averages theinput signals of the controllers for controlling the angles of thehydrofoils between safety constraints.
 20. Craft according to claim 19,wherein the control unit comprises an actuator for each hydrofoil. 21.Craft according to claim 20, wherein the hydrofoil actuators eachcomprise separate control and actuating elements supplied from separatepower sources integrated into a single unit.